The biological activity of chiral chemical compounds often depends upon their absolute stereochemical configuration, since a living body presents a highly enantioselective environment. Therefore, many racemic compounds show significant enantiomeric selectivity in pharmacokinetics and pharmacodynamics. Often a single enantiomer of a racemic mixture has a desired therapeutic effect while the enantiomer of opposite configuration may be ineffective or may even produce undesirable side effects. Awareness of this phenomenon intensified when the teratogenic effects of the drug thalidomide, once used as an anti-nausea medication for pregnant women, emerged in the 1960s. Thalidomide and many other chiral drugs had been sold for years as racemic mixtures. In 1992, the U.S. Food & Drug Administration (FDA) issued a policy on stereoisomeric drugs. Although the FDA allows racemates to be sold, the individual enantiomers must be characterized pharmacologically and toxicologically. It has been estimated that in 2006, 80% of small-molecule drugs approved by FDA were chiral and 75% were single enantiomers and, with increasing evidence of problems related to stereoselectivity in drug action, enantioselective analysis by chromatographic methods has become the focus of intensive research of separation scientists.
High performance liquid chromatography (HPLC) utilizing chiral stationary phases is the most popular method for determining the enantiomeric purity of chemical compounds on analytical columns or for isolating enantiomers on preparative columns. In the chemical and pharmaceutical Industries methods development often includes screening chiral compounds and potential impurities on analytical columns with numerous chiral phases.
Conventionally, chromatographic media utilizing the chirality of natural polysaccharide derivatives are widely known. Most commonly, the polysaccharide derivative is an ester derivative or carbamate derivative of cellulose or amylose. For example, U.S. Pat. No. 4,818,394 to Okamoto et al. discloses and claims various cellulose tribenzoates for the chromatographic resolution of optical isomers and U.S. Pat. No. 5,489,387 to Namikoshi et al. describes a chromatographic separation medium comprising cellulose tris-3-(3-pydridyl)acrylate. U.S. Pat. No. 7,223,334 to Okamoto et al. describes separating agent for enantiomeric isomers using cellulose tris(cyclohexylcarboxylate), cellulose tris(cyclopentylcarboxylate) or cellulose tris(cycloadamantylcarboxylate), while U.S. Pat. No. 7,156,989 to Okamoto et al. describes separating agents for enantiomeric isomers comprising amylose tris 5-indanylcarbamate. Also, U.S. Pat. No. 5,472,599 to Shibata discloses a chromatographic separating agent comprising dextran tribenzoates and U.S. Pat. No. 5,639,824 to Okamoto describes a chromatographic medium consisting of a chemically bonded body comprising a support and a highly substituted oligomeric cyclodextran derivative having a 3,5-dimethylphenylcarbamate constituent.
Although many polysaccharide derivatives have proven useful as chromatographic media, it is well known that such natural polysaccharides show considerable variation with respect to parameters such as molecular weight, proportions of the sugar monomer constituents, degree of branching and particular linkage types. In fact, few natural polysaccharides, if any, are monodisperse. Furthermore, polysaccharides such as cellulose, chitosan, amylose and the like, which are derived from different species or from different sources within a species, show significant variation in structure, chemical properties and molecular weight. Such variability of natural polysaccharides causes problems in the production of consistent chromatographic media and renders the chromatographic methods based on such media less that ideal. Since the synthetic, non-polysaccharide, carbohydrate polyethers of the present invention are essentially monodisperse and uniform in structure, the chromatographic media produced there from are consistent with potentially little or no batch-to-batch variability.
Many stationary phases for HPLC columns utilize polysaccharide derivatives supported on carriers such as alumina, zirconia or silica gel for the purposes of increasing the packing ratio of the separating agent into a column, facilitating handling, enhancing mechanical strength, and the like. The synthetic non-polysaccharide carbohydrate polymers of the present invention are amenable to the known techniques and methods employed to support the chiral selector on such carriers.
The derivatives of natural polysaccharides presently used as chromatographic stationary phases are most commonly coated onto carriers in thick layers, which results in processes wherein transport is slow and peaks are substantially broad. Furthermore, the use of natural high polymers or their derivatives as stationary phases requires the use of carrier particles of large pore-size and since such particles are fragile the operating pressure a high-pressure liquid chromatography (HPLC) system is limited. Therefore, there exists a need for improved non-polysaccharide polymeric materials for use in stationary phases effective for chromatographic separations via a variety of techniques, wherein such stationary phases have controllable and reproducible manufacturability.
There exists a need for chromatographic media that may prepared by methods that allow for a high degree of control of all molecular, chemical and physical properties of the stationary phase.
There exists a need for method for reproducibly providing non-polysaccharide based materials with control of relative hydrophilicity/hydrophobicity.
There exists a need for stationary phases effective for chromatographic separation that may be conveniently modified or custom synthesized to accommodate specific separation requirements.
There exists a need for low molecular weight non-polysaccharide based materials for use as stationary phases of chromatographic media that allow rapid mass transport and high capacity.
There also exists a need for new non-polysaccharide stationary phases effective in chromatographic separation of enantiomers to address increasing demand in the chemical and pharmaceutical industries.
The present invention addresses these and other needs.
Many drugs and other pharmaceutical and bioactive materials exhibit only limited solubility and/or stability in conventional liquid carriers and are therefore often difficult to formulate and administer. In many cases, multiple administrations are required to achieve a desired therapeutic effect for an extended period of time. Various dosage forms and polymeric drug delivery devices and have been investigated for long term, therapeutic treatment of various diseases.
Some polymers exhibit abrupt changes in aqueous solubility as a function of temperature. Certain of such polymers exhibit a lower critical solution temperature (LCST), wherein the interactive forces (e.g. hydrogen bonding) between water molecules and polymer molecules become unfavorable and phase separation occurs. Consequently, aqueous solutions of such polymers often display relatively low viscosity at ambient temperature and exhibit a sharp increase in viscosity following a small temperature increase, resulting in formation of a semi-solid gel. In certain polymers such a transition from a relatively low viscosity solution to a semi solid hydrogel occurs within in the range of mammalian body temperatures and therefore biodegradable embodiments of thermogelling (RTG) polymers have been investigated for use in a variety of biomedical applications such as drug delivery, tissue engineering, and wound healing. In such systems pharmaceutical agents are combined with an aqueous polymer solution at low temperature and, upon injection into a mammalian body, a hydrogel is formed such that the pharmaceutical agent can be released in a controlled manner. However, many of the RTG's examined to date have serious drawbacks for biomedical applications.
Cha et al. in U.S. Pat. No. 5,702,717 describe RTG systems wherein the polymers are block copolymers with a hydrophobic block comprising a poly(α-hydroxy acid) and poly(ethylene carbonate); and a hydrophilic block comprising poly(ethylene glycol). However, it appears that several of the disclosed hydrogels may not useful for biomedical applications since the lower critical solution temperature (LCST) for many of these gels is greater than 37° C.
Martini et al., J. Chem. Soc., 90(13): 1961-1966 (1994) describe low molecular weight ABA type triblock copolymers which utilize hydrophobic poly(ε-caprolactone) and poly(ethylene glycol). However, in vitro degradation rates for such copolymers are too slow for use in sustained-release systems.
Stratton et al., in WO 98/02142 describe compositions comprising polyoxyethylene-polyoxypropylene block copolymers having RTG properties for the delivery of proteins. However, such materials have limited in biomedical applications since they are toxic to body organs and are nonbiodegradable. Moreover, only high molecular weight polyoxyethylene-polyoxypropylene block copolymers at higher concentrations (15-25 wt. %) exhibit RTG properties.
Other known thermosensitive polymers include poly(ethylene oxide)/polypeptide conjugates and pH-sensitive chitosan/glycerol phosphate compositions. While the degradation products of polypeptides are neutral amino acids and there is no significant pH drop during polymer degradation, such polymers are usually difficult to reproducibly synthesize; and chitosan/glycerol phosphate compositions are known to have low MW components, which may diffuse from the gel causing phase separation of pH sensitive chitosan molecules. In general, natural polymers are much less desirable than synthetic polymers because of batch-to-batch properties variation.
Still other known thermosensitive polymers include water-soluble polyphosphazenes. However, such polyphosphazenes have limited utility since they are not are not readily biodegradable. While such water-soluble poly(phosphazenes) have been studied for drug delivery applications, storage time in aqueous solutions is limited by slow hydrolysis.
Thermosensitive water-soluble biodegradable polymers comprising polylactic acid (PLA) or polylactic acid/polyglycolic acid (PLA/PGA) blocks have been widely investigated for use in biomedical applications. However such compositions are known to generate lactic acid and glycolic acid upon biodegradation, wherein such acids may have adverse effects on acid sensitive drugs. Also, such biodegradable polymers have limited storage stability in aqueous solution.
Therefore, a need exists for thermosensitive biodegradable hydrogel-forming materials prepared by methods that allow for a high degree of control of all molecular, chemical and physical properties.
There exists a need for water-soluble biodegradable polymers for use in various biomedical applications such as delivery of drugs and other pharmaceutical and bioactive materials as well as for use in various food and beverage industries and the like.
Also, there exists a need for methods and processes for reproducibly production of non-polysaccharide based carbohydrate materials with control of relative hydrophilicity/hydrophobicity.
Furthermore, there exists a need for reverse thermogelling (RTG) materials that may be conveniently modified or custom synthesized to provide the degradation rates, sol-gel transition temperatures, critical gelation concentrations and permeability requirements for specific applications.
The present invention addresses these and other needs.